Artificial ventilation systems and components thereof, and methods for providing, assembling and utilizing same

ABSTRACT

A method for providing assisted ventilation which avoids hypoxia and hypocapnia in which a predetermined dead space in an assisted ventilation system is provided external to the patient. The method may also be used to create normocapnia or moderate hypercapnia without causing hypoxia during assisted ventilation. Improved assisted ventilation devices, including an improved proximal terminal, improved tubular attachments and improved coaxial filters, are disclosed which are safer and less expensive to use than corresponding prior art unilimb assisted ventilation devices. Connector fittings and adapters to provide connector fittings on assisted ventilation devices are disclosed which provide positive indication of attachment of assisted ventilation devices and resist detachment of assisted ventilation devices. The devices of the present invention also reduce medical waste in comparison to prior art assisted ventilation devices. An interface is provided which incorporates the proximal terminal and other functional devices to which tubular respiratory conduits of predetermined and/or adjustable dead space volumes can be attached.

RELATED U.S. APPLICATION DATA

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/018,540, filed Feb. 4, 1998, now U.S. Pat. No. 5,983,896,issued Nov. 16, 1999, which was a divisional application of U.S. patentapplication Ser. No. 08/751,316, filed Nov. 18, 1996, now U.S. Pat. No.5,778,872, issued Jul. 14, 1998.

FIELD OF THE INVENTION

The present invention relates in one aspect to artificial ventilationmethods and systems for administering and exhausting gases to a mammal,including methods and systems for use in anesthesia and administrationof oxygen to patients, and more particularly to artificial breathingsystems capable of controlling carbon dioxide rebreathing. The presentinvention relates in another aspect to a unilimb inspiratory andexpiratory breathing device for use in a breathing circuit, which hasone or more tubular conduits detachable at a common interface, theinterface optionally providing for control of gas flow and operableconnection to different functional devices. The present invention alsorelates to improved components of assisted ventilation systems andmethods for providing same.

BACKGROUND OF THE INVENTION

Breathing circuits are utilized to conduct inspiratory gases from asource of same, such as from an anesthetic machine, to a patient, and toconduct expiratory gases away from the patient. The gases are conductedthrough two or more conduits, and, generally, at least a portion of theexpiratory gas is recycled to the patient after removal of carbondioxide. To facilitate description of the prior art and the presentinvention, the end of a conduit directed toward a patient shall bereferred to as the distal end, and the end of a conduit facing orconnected to a source of inspiratory gases shall be referred to as theproximal end. Likewise, fittings and terminals at the distal end of thebreathing circuit, e.g., connecting to or directed at the patient airwaydevice (i.e., endotracheal tube, laryngeal mask, or face mask), will bereferred to as distal fittings or terminals, and fittings and terminalsat the proximal end of the breathing circuit will be referred to asproximal fittings and terminals. For further information on breathingsystems, and anesthetic and ventilation techniques, see U.S. Pat. No.3,556,097; U.S. Pat. No. 3,856,051; U.S. Pat. No. 4,007,737; U.S. Pat.No. 4,188,946; U.S. Pat. No. 4,232,667; U.S. Pat. No. 5,284,160;Austrian Patent No. 93,941; Dorsch, J. A. and Dorsch, S. E.,Understanding Anesthesia Equipment: Construction, Care AndComplications, Williams & Wilkins Co., Baltimore (1974) (particularlychapters 5-7); and Andrews, J. J., “Inhaled Anesthetic DeliverySystems,” in Anesthesia. Fourth Edition, Miller, Ronald, M. D., Editor,Churchill Livingstone Inc., New York (1986) (particularly pp. 203-207).The text of all documents referenced herein, including documentsreferenced within referenced documents, is hereby incorporated as ifsame were reproduced in full below.

U.S. Pat. No. 4,265,235, to Fukunaga, describes a unilimb device ofuniversal application for use in different types of breathing systems,which provides many advantages over prior systems. The Fukunaga systemutilizes a space saving coaxial, or tube-within-a-tube, design toprovide inspiratory gases and remove expiratory gases. Generally, theinner tube is connected at its proximal end to a source of inspiratory,fresh gas, while the outer tube proximal end is connected to an exhaustport and/or to a carbon dioxide absorber (the latter at least partiallyexhausts into the inspiratory gas source when used in a circle system).In addition to reducing the size of the breathing apparatus connected toa patient by reducing the number of tubes near the patient, the Fukunagasystem has additional benefits, such as serving as an artificial nose(expired air warms and humidifies inspired air as the opposing two flowsare co-axial in the unilimb device). The Fukunaga circuit is also saferthan prior co-axial systems, since the distal end of the inner tube isnot connected to the outer tube at a distal fitting, so that the outertube can be axially extended with respect to the inner tube withoutdisconnecting the proximal end of the inner tube from the source ofinspiratory gases; this safety feature can also be used to increase thedead space between the distal ends of the inner tube and outer tube, andthereby allow for adjustment of the amount of expiratory air the patientrebreaths. Dead space is defined herein as the part of the breathingcircuit external to the patient which, at the end of expiration, isfilled with exhaled gases to be inhaled at the next breath (generallythe expired air in the dead space is combined with oxygen and/or othergases provided from a source thereof). It will be appreciated that mostknown breathing circuits provide a certain amount of dead space whenbeing used. For example, in the device shown in Leagre et al., U.S. Pat.No. 5,404,873, the portion of the breathing circuit that is distal tothe end to the inspiratory tube. plus the area between the face mask andthe patient's face all comprises dead space where inspiratory andexpiratory gases are mixed. The same is true for the device shown inLeagre, U.S. Pat. No. 5.901,705, except that the dead space alsoincludes the interior volume of the filter.

An embodiment of the Fukunaga unilimb device is commerciallymanufactured as the UNIVERSAL F™ by King Systems Corporation ofNoblesville, Ind., USA. The device includes a proximal terminalcomprising a hollow, T-shaped housing with three ports: an inspiratorygas port, an expiratory gas port at a perpendicular angle to theinspiratory gas port, and a third (“patient”) port. The proximalterminal is connected to an outer tube and a coaxial inner tube, whichcarry gases to and from the proximal terminal. The outer tube isflexible and corrugated, and formed of a transparent (orsemi-transparent) material. The proximal end of the outer tube issealably connected and bonded to the patient port of the proximalterminal. The proximal end of a dark colored, flexible inner tube isscalably connected and bonded to the inspiratory port, and extendsthrough the T-shaped housing, out the patient port, and passes throughmost of the axial length of the outer tube. The dark color of the innertube readily permits the user to see through the outer tube to determinewhether the inner tube is properly connected.

The inner diameter of the outer tube is sufficiently larger than theouter diameter of the inner tube to permit adequate patient respiration.The distal end of the outer tube is scalably connected and bonded to theexterior of an annular housing which forms a distal terminal. Theannular housing of the distal terminal is designed to prevent the distalend of the inner tube from extending beyond the distal end of the outertube. The entire unit is designed for disposal after a single use.

The UNIVERSAL F™ device offers great advantages over prior dual line andunilimb anesthesia circuits, and respiratory assist devices. However,manufacture of the entire unit requires several complex steps, and mustbe done with care so that the inner and outer tubes are properly sealedand bonded to the proximal terminal ports at their proximal ends; it isparticularly important that the inner tube proximal end be firmlyconnected to the proximal terminal (at the inspiratory port) when theinner tube carries inspiratory gases, since disconnection during use maynot allow sufficient oxygen and/or anesthetic gases to reach a patient,which is highly undesirable.

While U.S. Pat. No. 4,265,235, to Fukunaga, teaches that the tubes andterminals of such a unilimb device can be detachable from one another,in practice, the proximal end of the inner tube is firmly bonded to theinspiratory port, since there remains a risk that the proximal end ofthe inner tube could be disconnected from the inspiratory port duringuse if a pressure fit (or friction fit) alone is used. Even ifdetachment of the inner tube is detected, the design of prior artunilimb devices does not facilitate the reconnection of the inner tubeto the inspiratory port of the proximal terminal due to the need to passthe inner tube proximal end through the length of the proximal terminalvia the patient port so that it can reach and be connected to theinspiratory port. Thus, the unilimb devices currently used generallycomprise a proximal terminal having an integrally connected inner tubeand outer tube.

Due to its single-use design, the entire unilimb device, including thedistal terminal, proximal terminal, inner tube and outer tube, isdisposed of after a single use, along with multiple devices usuallyconnected to the patient nozzle, such as a CO₂ monitor (capnometer),temperature and humidity controlling and monitoring devices, an O₂controlling and monitoring device, and an infection controlling device(e.g., a filter). Thus, in addition to the inconvenience of requiringfittings (or a housing accommodating same) for these additional devicesat the patient nozzle or distal terminal, replacement of these fittings,tubing, and devices after a single use is expensive, and contributes toever-growing medical wastes, which are sometimes difficult to finddisposal sites for. All of the systems described in the aforementionedpatents suffer from similar deficiencies. Therefore, there is a need foran improved unilimb device and ventilation system which reduces costsand helps the environment by reducing waste. There is also a need tosimplify the construction, and to increase the safety, efficacy, andreliability of such devices.

Further, it is believed that devices sold for disposal after a singleuse may sometimes be reused in order to save costs, which may endangerpatients. Efforts have been made to make it safer to reuse some patientrespiratory conduit components. One problem with this is that theexterior of the patient respiratory conduits, as well as the interiorthereof, need to be protected from contamination, so that contaminantsfrom a first patient do not get passed on to subsequent patients byadhering to the exterior of reused components. For example, the devicedescribed in Fukunaga U.S. Pat. No. 4,265,235, discussed above, has acoaxial conduit, which can be connected at its distal end (i.e., patientend) to a filter in order to protect the interior of the coaxial conduitfrom being contaminated. However, the filter does not protect theexterior of the coaxial conduit from contamination. One approach toreducing contamination on the exterior of the conduit is shown in U.S.Pat. No. 5,901,705, to Leagre, in which a sleeve extends proximally froma distal (i.e., patient end) filter over the patient respiratory conduitso that at least the portion thereof nearest the patient is not exposedto contamination from the patient. The device shown in the Leagre '705patent places a disposable filter at the patient end of the device. TheLeagre device is designed to enable the breathing circuit to be reusedon successive patients since the filter and sleeve prevent contaminationfrom entering the breathing circuit from the patient; and preventcontamination in the breathing circuit from entering the patient. Thusthe Leagre '705 patent teaches that the replacement of the relativelyinexpensive, one-time-use filter and sleeve between patients permits therelatively more expensive breathing circuit to be used with multiplepatients.

Breathing systems generally provide oxygen to a patient, while removingcarbon dioxide produced by the patient. For example, in anesthesia, orintensive care, the patient is provided an artificial breathingatmosphere, in which the physician provides a mixture of gases to thepatient. In addition to providing oxygen and a variety of vaporizedanesthetic agents to the patient, the physician may permit the patientto rebreath some expired gases. Rebreathing simply consists of inhalinggases which have been expired, including carbon dioxide. However,assisted respiration/ventilation to a patient must be safe, and hypoxia(i.e., patient oxygen deficiency) must be avoided. Therefore,inspiratory gases are generally provided at high enough pressure, tidalvolume and respiratory rate (hyperventilation) to ensure that hypoxiaand atelectasis (lung alveolar collapse) is avoided. Thus, patients aregiven very high inspired concentrations of oxygen to avoid hypoxia, butunfortunately they often experience abnormally low carbon dioxide levels(i.e., hypocarbia or hypocapnia), and insufficient carbon dioxide canhave a negative impact on vital organs (e.g., brain, heart, splanchnicorgans, etc.). However, many physicians believe that increasing arterialcarbon dioxide partial pressure (P_(a)CO₂, also referred to as arterialcarbon dioxide tension, often reported as mmHg) in patients byincreasing the carbon dioxide breathed by the patient (e.g., byincreasing the amount of rebreathing) would cause hypoxia. Thus, it wasbelieved that hypercapnia during assisted ventilation was harmful, sinceit was believed it would be associated with hypoxia. Further,hypocapnia, while it can be harmful, was believed to be less harmfulthan hypoxia. Therefore, there remains a need for an improved artificialventilation method which controls or avoids hypocapnia withoutcompromising vital organ tissue perfusion or oxygenation (i.e., avoidshypoxia).

Further, there is a need to increase safety of assisted ventilationsystems by reducing the possibility of component disconnections duringuse, a need to increase the likelihood that components provided forsingle-use only are not reused, and that devices, such as filters, meetminimum standards to be used in assisted ventilation systems (as usedherein, the terms assisted ventilation system and/or artificialventilation system refer to any device which provides inspiratory gasesto a patient and/or receives expiratory gases from a patient, such asbut not limited to anesthesia machines, artificial ventilators, etc.).

SUMMARY OF THE INVENTION

The present invention provides in one aspect an improved assisted orartificial ventilation system utilizing a unilimb device for providingand exhausting gases from a mammal, and, in another aspect, anartificial ventilation method which avoids hypocapnia and hypoxia.Further aspects of the present invention include new and improveddevices for use in the ventilation methods and systems of the presentinvention.

Aspects of the present invention relate to the surprising discovery bythe inventor that concerns about disconnection of the inner respiratorytube, when connected to the inspiratory port of a proximal terminal inbreathing circuits utilizing a unilimb device, such as the UNIVERSAL F™circuit or the “Bain” circuit (U.S. Pat. No. 3,856,051), can beeliminated by the new proximal terminal construction of the presentinvention, which facilitates the use of tubing which is intentionallymade to be readily attachable and detachable to the proximal terminalports, rather than permanently sealably connected as in present systems,and yet provide improved function, safety, and serviceability. Thebreathing circuit manufacturing process is greatly simplified byeliminating the steps of sealably bonding the proximal ends of the innerand outer flexible respiratory tubes to the inspiratory and patientports, respectively, of the unilimb proximal terminal. The new unilimbproximal terminal of the present invention facilitates the attachmentand detachment of respiratory tubing to the proximal terminal, thusresulting in a cheaper and safer breathing circuit. The new unilimbproximal terminal also permits more efficient placement and utilizationof the other breathing circuit components in a multifunctional interfaceincorporating the unilimb proximal terminal. In another aspect of thepresent invention, an improved coaxial tube device is provided, which isreadily attachable and detachable from the new proximal terminal. Theimproved coaxial tube device has an inner tube in fixed spaced coaxialparallel relationship to an outer tube at its proximal end, such that asingle step is required to connect both tubes to the proximal terminal.This is made possible by a fitting within or at the proximal ends of thecoaxial inner and outer tubes, which still permits the distal end of theinner tube to axially move with respect to the distal end of the outertube. As used herein, coaxial refers to the fact that one tube iscontained within the other, but the central axis of both tubes need notbe aligned.

Aspects of the present invention involve the surprising discovery by theinventor that hypoxia can be avoided while simultaneously creatingintentional dead space in the breathing circuit, thereby increasingrebreathing of expired carbon dioxide, which enables maintenance ofnormal levels of arterial blood carbon dioxide (i.e., normocapnia)during artificial ventilation. Even more surprising is the discovery bythe inventor that moderate hypercapnia will not cause hypoxia, providedsufficient oxygen reaches the patient; in fact, moderate hypercapnia canbe beneficial to a patient (e.g., improve cardiovascular oxygenavailability and tissue oxygenation). In yet another aspect of thepresent invention, the arterial blood carbon dioxide tension (P_(a)CO₂)can be predictably controlled via a predetermined dead space created inthe unilimb device breathing tubes (i.e., the volume in the outer tubedefined by the space between the outer tube distal end and the innertube distal end). The dead space volume may be made adjustable by use ofaxially extendable and compressible corrugated tubing (which does notrebound to its prior length and maintains its approximate internaldiameter despite bending and/or axial length changes): the tubingconnects at its proximal end to the patient port of the proximalterminal, and may have dead space calibration markings thereon to permitdetermination and adjustment of dead space volume contained therein.

In another aspect, the present invention includes an artificialventilation method which avoids hypocapnia and hypoxia. The methodcomprises provision of artificial ventilation to a mammal (in which themammal inspires and expires spontaneously or with mechanical assistance)sufficient to prevent hypoxia, while permitting a sufficient portion ofthe mammal's expiratory gases to be rebreathed to allow the arterialcarbon dioxide tension of the mammal to be between about 35 mmHg toabout 45 mmHg (i.e., normocapnia for a human). In another aspect, themammal's expiratory gases are rebreathed sufficiently to permit thearterial carbon dioxide tension to be between about 45 mmHg to about 95mmHg (i.e., moderate hypercapnia). This surprising invention includesnew artificial ventilation tubing and/or filters, and methods forproviding same, which permits the user to provide sufficient oxygenationand carbon dioxide to a patient, while using a minimum amount ofdisposable, single-use materials.

Another aspect of the present invention includes an improved unilimbdevice useful in providing the above artificial ventilation method. In apreferred embodiment, a unilimb device for use in a breathing circuitincludes an outer tube, and an inner tube, each having a proximal endand a distal end. The outer diameter of the inner tube is smaller thanthe inner diameter of the outer tube, wherein the outer tube can beoperably connected at its distal end to a fitting (e.g., endotrachealtube or mask) that can provide artificial ventilation to a mammal. Theinner tube is at least partially disposed within the outer tube, and thedistal end of the inner tube is disposed within and in direct fluidcommunication with the outer tube. The proximal end of one of the tubesis connected to an inspiratory gas input (preferably the inner tube),and the proximal end of the other tube is connected to an exhaustoutlet. The distal end of the inner tube is axially disposed at apredetermined distance from the distal end of the outer tube to create adead space in the outer tube between the tube distal ends. The deadspace permits the mixing of inspiratory (fresh) gases with expiratorygases from a patient operably connected to the device, and thereby theamount of gases rebreathed by a patient can be related to the dead spacevolume. This dead space can be predetermined and adjusted to provide fornormocapnia or moderate hypercapnia while avoiding hypoxia. In apreferred embodiment, an inner tube and outer tube are provided, which,when operably connected to a mammal to provide respiration, the deadspace external of the patient is at least 10 cubic centimeters, and inanother preferred embodiment at least 30 cubic centimeters. This deadspace may be as small as 10 cubic centimeters for normocarbia in a smallmammal (e.g., a human infant), and may exceed 150 cubic centimeters inlarger mammals (e.g., adult humans). As used herein, and as isconventionally understood, dead space may also be defined as that volumein a patient respiratory conduit external of a patient and distal of themost distal source in or connected to the patient respiratory conduit offresh inspiratory gases to the patient, and includes the space in theconduit(s) and devices external of the patient; for example, if a singlepatient respiratory conduit carries inspiratory and expiratory gases,dead space is the volume in the patient respiratory conduit between thepatient and the inspiratory gas inlet, and any filters or other devicestherebetween. If, for example, a coaxial patient respiratory conduit isused (which, for example, has an outer flexible conduit for carryingexpiratory gases from a patient operably connected to the distal endthereof), and the inner flexible tube of the coaxial patient respiratoryconduit is connected to an inspiratory gas inlet, then the volume in thepatient respiratory conduit (and any fittings, filters and otherdevices) between the patient and the distal end of inner flexible tubeis dead space.

Since it is desirable to have the assisted ventilation system at adistance from the patient to permit health care personnel better accessto the patient, in one embodiment of the present invention, the coaxialtubing is of considerable length, and has little or substantially nodead space therein; the distal end of the inner flexible tube is biasedagainst or bonded to a distal fitting connected to the end of the distalend of the outer flexible tube. A dead space tube can be operablyconnected to the distal end of the coaxial flexible tubing; in apreferred embodiment, the dead space tube is connected to a distalfitting at the end of the coaxial tubing. The dead space tube can beoperably connected through a filter (having a predetermined dead spacetherein) at its proximal end to the distal fitting at the distal end ofthe coaxial tubing (thus filtering both inspiratory and expiratorygases), or the filter may be connected at the distal end of the deadspace tube. Thus, a coaxial flow of inspiratory and expiratory gases maybe directed through a single filter and dead space tube. in anotherembodiment, the inner tube of the coaxial conduit is of a fixed lengthand preferably of a dark color (or has a dark colored band about itsdistal end); the outer tube can have its length adjusted, and is made ofa clear (transparent or semi-contraction of the outer tube to alter theaxial distance between the distal end of the outer tube and the distalend of the inner tube. The outer tube can be formed of a section ofcorrugated tubing, such as for example FLEXITUBE®, which upon axialextension from its compressed axial conformation, or vice versa, willretain its axial length (e.g., will not rebound; i.e., accordion-likepleated tubing). Further, the FLEXITUBE®, when bent, will retain theangle of curvature it is bent to without substantial reduction in thetube's inner diameter. (Suitable corrugated tubing for use in thepresent invention is used in the Ultra-Flex circuit from King SystemsCorporation, of Noblesville, Ind., U.S.A.). The inner tube can be seenthrough the outer tube and, in one embodiment, the dead space volume canbe determined by reference to calibration markings, which are on theouter tube, aligned with the distal end of the inner tube. By placementof a biological contamination filter between the distal ends of theinner and outer tubes and the patient port of the proximal terminal ofthe unilimb device, the current invention makes it possible to safelyextend the service life of the proximal terminal beyond a single use. Anexample of suitable prior art biological contamination filter means,which can be used in some embodiments of the present invention, is theVIROBAC II Mini-Filter by King Systems. Likewise, other adapters and avariety of single use devices, previously connected at the distal orpatient fittings, can be reused by connection to the interface at theproximal side of the biological contamination filter. Since the proximalterminal is more complicated to manufacture, this invention permitssubstantial cost savings by permitting reuse of the proximal terminaland other devices connected thereto, while simultaneously reducingenvironmental (medical) wastes.

In another embodiment, patient safety is enhanced by provision of uniqueconnector fittings for connecting components of assisted ventilationsystems, for example for connecting tubing and filters. For example, aunique proximal connector fitting on a filter matches and connects to amating fitting on the distal end of either a single or coaxial patientrespiratory conduit. The mating fitting on the distal end of a patientrespiratory conduit may be provided with a locking device to preventaccidental disconnection. Further, patient respiratory conduits andproximal terminals may also be provided with a blocking device toprevent an unmatched dead space tube, filter, or other devices frombeing connected thereto. Thus, for example, only filters meeting minimumrequirements can be connected to single or coaxial patient respiratoryconduit having a mating fitting. In addition to filters, other devicesmay be provided with unique connector fittings corresponding to theunique fittings on the distal end of the patient respiratory conduit. Inanother embodiment of the present invention, an adaptor is provided, inwhich the distal end has a standard patient device connector toaccommodate standard filters and patient airway devices (e.g.,endotracheal tube proximal end), and the proximal end has a uniqueconnector fitting for a mating connector on the distal end of a patientrespiratory conduit.

In yet another aspect, the present invention includes a system for usein mammals to provide respiratory and other gases. The system comprisesa first breathing conduit having a proximal end and a distal end forproviding and exhausting respiratory gases from a mammal. and aninterface comprising a breathing circuit operably connected to theproximal end of the first breathing conduit. A biological contaminationfilter blocks biological contaminants in the first breathing conduitfrom communicating with the interlace components while allowing foradequate transmission of inspiratory and expiratory flows.

The biological contamination filter can be located within the proximalend of the first breathing conduit, or serve as a separate detachablecomponent. In one embodiment of the present invention, a coaxial filterapparatus is provided. The filter apparatus comprises an inner housinghaving openings at its opposite ends; at least one of the openings hasan internal diameter which equals the internal diameter of the innertube of the breathing conduit, so that the filter device may be attachedin a coaxial fashion with the inner tube of the breathing conduit. Theinner diameter of the filter device inner housing expands to form achamber which accommodates a filter having a predetermined diameter topermit sufficient flow therethrough (i.e., flow resistance is inverselyproportional to filter surface area). The inner housing is containedwithin, and in spaced parallel relationship with, an outer housing whichis similar or identical in shape, but of sufficiently greater internaldiameter throughout to permit fluid to flow between the outer walls ofthe inner housing and the inner walls of the outer housing. A singledisc shaped filter may be contained within the inner housing andradially extend from within the inner housing chamber lo the outerhousing chamber, or a filter in the shape of an annular ring may bedisposed about the outer diameter of the inner housing filter chamberand extend to the inner wall of the outer housing chamber. The inner andouter filter housings may each be constructed from two funnel shapedcomponents, a pre-filtration housing and postfiltration housing (whichare mirror images of each other). the two components can be assembledtogether after placing a filter therebetween at the center of the filterchambers to be formed thereby.

A preferred embodiment of the proximal terminal interface comprises aT-shaped housing, having an inspiratory gas input (inspiratory port), anexpiratory gas outlet (expiratory port), and a first respiratory(patient) port. The first respiratory port can be placed in fluidcommunication, through the biological contamination filter, with a firstbreathing (respiratory) conduit leading to a patient. The inspiratoryport of the proximal terminal connects to and is integral with aninternal conduit, which passes through the housing of the proximalterminal, so that the distal end of the internal conduit forms a secondrespiratory port, which terminates within the first respiratory port.The second respiratory port has a smaller diameter than the firstrespiratory port, so that gases may flow through the first respiratoryport and through the space between the exterior wall of the innerconduit and the interior wall of the proximal terminal housing. The newproximal terminal of the present invention permits the ready connectionand disconnection of an inner tube of a coaxial respiratory conduit tothe inspiratory gas source, since direct sealed fluid communication withthe inspiratory port is greatly facilitated by the inner conduit of thenew proximal terminal housing. Thus, the prior art difficulties withconnection of the inner tube of unilimb devices to the inspiratory portarc eliminated, making it possible to avoid sealably bonding the innerflexible respiratory tube to the inspiratory port of the proximalterminal during manufacture.

It is noted that in preferred embodiments of unilimb ventilationdevices, the inner tube carries inspiratory gases from an inspiratorygas source, and the outer tube carries expiratory gases. Generally, itis desired that inspiratory gas flow be laminar, while the expiratorygas flow should be turbulent. Turbulent expiratory gas flow isfacilitated by the annular shape of the passage between the inner wallof the outer tube and outer wall of the inner tube, as well as by theconfluence of gases exiting from the inner tube distal end into the deadspace with expiratory air. Further, filtration of the expiratory gasesincreases turbulent flow in the outer tube, causing a positive endexpiratory pressure (PEEP) effect, which helps to maintain positivepressure in the patient airway (to prevent atelectasis). Thus, thecoaxial filter apparatus of one embodiment of the present inventionhelps create turbulent flow in the expiratory gases, when the outer tubeis used as the expiratory gas conduit.

In one embodiment, the first breathing or respiratory conduit includesone tube, referred to herein for simplicity as the outer tube, and has afirst (proximal) end and a second (distal) end. The outer tube isconnected at its first end through a filter device to the firstrespiratory port, and has its second, or distal, end directed toward thepatient. Both the first and second respiratory ports terminate in andare in fluid communication with the proximal end of the outer tubethrough one or more biological filters. Thus the first breathing conduitbetween the patient and the proximal terminal can comprise a singletube, the entire length of which provides a dead space, or mixingchamber for inspiratory and expiratory gases. The first breathingconduit is detachable from the proximal terminal for disposal orsterilization. Use of this system reduces costs and waste, since onlythe breathing conduit is designed for single use. Another advantage isthat the proximal terminal of prior art unilimb devices, such as theUNIVERSAL F™, is no longer disposed of after a single use. and may be apermanent part of the interface.

In one embodiment of the present invention, the respiratory conduit maycomprise an outer flexible tube, the length of which can be preselectedfrom various lengths to vary the dead space to a preselected volume. Inanother embodiment, the outer tube can be axially expandable andcompressible (i.e., have accordion-like pleats) to make the dead spaceadjustable; the dead space can be determined by reference to calibrationmarkings on the outer tube. The calibration markings on the pleated tubemay be concealed in the folded pleats, and revealed in opened pleats.The calibration markings may be color-coded bands.

In another aspect of the present invention, the first breathing conduitfurther comprises an inner flexible tube axially disposed within theouter flexible tube. The inner tube proximal end is connected through abiological contamination filter to the second respiratory port, and thedistal end of the inner tube terminates inside of the outer tube. Thedead space can be adjusted by adjusting the axial distance between theouter tube distal end and inner tube distal end. In one embodiment, theproximal end of the flexible inner tube and the proximal end of theflexible outer tube are held in spaced parallel coaxial relationship bya rigid fitting, formed of coaxial rigid annuli, a smaller annuluswithin a larger annulus. which are held in fixed spaced relationship byrigid radial struts extending from the exterior of the inner annulus tothe interior of the outer annulus; in one embodiment, the struts do notextend to the ends of the inner annulus to permit a flexible conduit tobe connected thereover. In a preferred embodiment, the fitting connectsto the distal end of a filter device, which has a threaded or flangedconnector at its proximal end to permit secure attachment to, and simpledetachment from, the first and second respiratory ports. In a preferredembodiment, the internal conduit of the interface proximal terminalcarries inspiratory gases to the second respiratory port, and the outertube of the interface carries expiratory gases entering from the firstrespiratory port. The inner and outer tubes may be of predeterminedlengths to provide a predetermined dead space, or the outer tube may beof variable length to permit adjustment of the dead space (or anextension added to the outer tube, with the extension having a fixed oradjustable volume or dead space); calibration markings on a clear outertube may be aligned with the end of the inner tube to determine deadspace volume.

The provision of readily accessible first and second respiratory portsin the distal end of the proximal terminal permits biological isolationof the first breathing conduit, whether it comprises only an outer tubeconnected to the first respiratory port, or a coaxial outer tube andinner tube, which are connected to the first and second respiratoryports, respectively. Thus, only the filter and first breathing conduitneed be disposed of (or sterilized) after a single use. The newinterface of the present invention permits numerous monitoring andcontrol devices to be included in the interface at the proximal end ofthe biological filter(s). Various devices contained in detachablemodules can be repeatedly utilized with the interface, including deviceswhich were formerly attached to the patient nozzle and disposed of aftera single-use. Thus, the new assisted ventilation system of the presentinvention provides for greatly simplified construction of disposableunilimb single use components, which reduces costs of production and atthe same time reduces the quantity of materials requiring replacementafter a single use. Further, fewer devices need be crowded about thepatient, providing improved surgical safety (less clutter at the patientmakes for easier surgical access and safety). Insertion of monitoringand control devices at the proximal, post filtration, end of thebreathing system, permits improved control and monitoring of thepatients' respiration with a simpler device.

Therefore, the present invention provides a simpler artificialventilation system, that is easier and less expensive to construct thanprior art systems, is easier, safer and less expensive to use, yetprovides improved features. Further, the present invention makespossible safer artificial ventilation by providing means and a methodfor simultaneously preventing hypoxia and hypocapnia. Further detailsand advantages of the present invention will be appreciated by referenceto the figures and description of exemplary embodiments set forthherein.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan and partial cross sectional view of a prior artassisted ventilation system utilizing a unilimb inspiratory andexpiratory gas conduit;

FIG. 2 is a cross-sectional view of a Fukunaga unilimb inspiratory andexpiratory gas conduit and proximal terminal as described in detail inU.S. Pat. No. 4,265,235;

FIG. 3A is a cross-sectional perspective view of the new proximalterminal of the present invention, which includes an inner conduitconnected to a second respiratory port;

FIG. 3B is a cross-sectional perspective view of an alternativeembodiment of the new proximal terminal illustrated in FIG. 3A;

FIG. 4 is an exploded plan view of an assisted ventilation system, withoptional components, in accordance with the present invention, includingan interface and patient breathing conduits;

FIG. 5A is a cross-sectional view of an embodiment of a detachablepatient coaxial breathing conduit for use in an assisted ventilationsystem in accordance with the present invention, such as the system ofFIG. 4;

FIG. 5B is a cross-sectional view of an alternative embodiment of thedetachable patient coaxial breathing conduit illustrated in FIG. 5Awhich includes a proximal extension;

FIG. 6A illustrates a perspective, partial cross-sectional view of anembodiment of a coaxial filter device for use in an assisted ventilationsystem in accordance with the present invention;

FIG. 6B is a perspective, partial cross-sectional view of an alternativeembodiment of the coaxial filter device illustrated in FIG. 6A.

FIG. 7 is a graphic illustration of the relationship between dead spacevolume, V_(D), and the resulting change in patient arterial carbondioxide tension, P_(a)CO₂, including a linear regression analysis curve,yielding a correlation coefficient, r, of 0.671, and a predicted valuefor the change in P_(a)CO₂ equal to the product of 2.621 times theV_(D), added to 1.766; this graph illustrates that the change inP_(a)CO₂ can be reliably predicted as a function of V_(D) (when V_(D) isbetween 0 and 8 ml per kg of patient weight, or cc³/kg);

FIG. 8 is a graphic illustration of the independence of P_(a)CO₂ asV_(D) was varied between about 0 and 8 ml/kg, including a linearregression analysis curve which shows no significant correlation betweenthe two variables in the range tested;

FIG. 9 is a graphic illustration of the independence of changes inP_(a)CO₂ and P_(a)CO₂ as P_(a)CO₂ was varied between 0 and 25 mmHg,including a linear regression analysis curve having a correlationcoefficient, r, of 0.153, thus showing that increasing P_(a)CO₂ between0 and 25 mmHg has no significant effect on P_(a)CO₂;

FIG. 10 is a table for estimating the increase in arterial blood carbondioxide tension in relation to rebreathing circuit apparatus dead space;

FIG. 11 is a plan view of an assisted ventilation system using a priorart dual hose fitting connected through a filter to a single patientconduit;

FIG. 12 is a partial cross-sectional view of the new proximal terminalillustrated in FIG. 3A connected to the detachable patient coaxialbreathing conduit illustrated in FIG. 5A, which in turn is connected toa filter and a dead space tube;

FIG. 13 is a plan view of a dead space tube connected to a filter;

FIG. 14 is a plan view of an alternative embodiment of the device ofFIG. 13 which includes a connector fitting at its proximal end;

FIG. 15 is an end elevation view of a distal connector fitting for usein alternative embodiments of the present invention;

FIG. 16 is a perspective end elevation view of an adapter for use withthe distal connector fitting of FIG. 15;

FIG. 17 is a plan view of an assisted ventilation system using a priorart dual hose fitting connected at its proximal ends to two filters andat its distal end to a single patient conduit,

FIG. 18 is a plan view of an assisted ventilation system using a priorart dual hose fitting connected to a single patient conduit at itsdistal end, and having a filter connected at the distal end of thesingle patient conduit;

FIG. 19 is an exploded partial cross sectional partial plan view of athreaded adapter and the distal end of conduit including a matingthreaded connector fitting;

FIG. 20 is partial cross-sectional view of the new proximal terminalillustrated in FIG. 3A connected to a detachable dead space tube;

FIG. 21 is partial cross-sectional view of the new proximal terminalillustrated in FIG. 3A connected to a detachable dead space tube whichin turn is connected to a filter; and

FIG. 22 is partial cross-sectional view of the new proximal terminalillustrated in FIG. 3A connected to a filter which in turn is connectedto a detachable dead space tube.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A brief description of a basic prior art artificial ventilation systemand unilimb device will facilitate a description of the presentinvention. With reference to FIG. 1, a schematic view of a circlecircuit artificial ventilation system utilizing a unilimb respiratory(inspiratory and expiratory) gas conduit is illustrated. A unilimbrespiratory (or breathing) conduit 1 may be attached at outlet 2(otherwise referred to as a nozzle or distal terminal) to a patientendotracheal tube or mask. Breathing conduit I is formed to include anouter tube 4 and an inner tube 5. Directional arrows 7 show thepreferred direction of gas flow through the system; for example,expiratory air is carried away from a patient through the annularspacing between inner tube 5 and outer tube 4. Inspiratory gases areprovided to inner tube 5 from a gas source 8, passing through aunidirectional valve 9. Inner tube 5 penetrates the wall of proximalterminal housing 11; housing 11 essentially comprises a bend in outertube 4, and the outer wall of tube 5 may be integrally sealed thereto.

A carbon dioxide absorber 13 may be used to remove carbon dioxide fromexpiratory gases passed therethrough, and the thus-filtered gasescombined with inspiratory fresh gases from source 8. Expiratory gasespass from a patient outlet 2 through outer tube 4, then throughunidirectional valve 15 to be recirculated or vented at exhaust port 17.

With reference to FIG. 2, a Fukunaga unilimb device, such as thatdescribed in detail in U.S. Pat. No. 4,265,235 is illustrated. Thedevice comprises a T-shaped proximal terminal 20, a distal terminal 30,a flexible inner tube 40, and a flexible outer tube 50. Since thediameter of inner tube 40 is smaller than the diameter of outer tube 50,an annular space 41 is formed therebetween. The distal end 51 of outertube 50 is connected to distal terminal 30, which has means 31 forpreventing the distal end 42 of inner tube 40 from extending beyonddistal terminal 30. The distal end 42 of inner tube 40 is free ofterminal 30 and outer tube 50.

The T-shaped housing of proximal terminal 20 includes an inspiratoryport 22, an expiratory port 24, and a patient port 26. Inner tube 40 isconnected at its proximal end to inspiratory port 22, and passespartially through proximal terminal 20 and out of patient port 26. Inpractice, the remote location of inspiratory port 22 from patient port26 makes it desirable to scalably bond the proximal end 28 of inner tube40 to inspiratory port 22, or, optionally, a continuous length of innertube 40 extends proximally of inspiratory port 22, and distally ofpatient port 26 to at or near distal end 51 of outer tube 50 (inner tube40 acting to seal, or being sealably bonded to, inspiratory port 22 atthe point of intersection therewith). Likewise, in order to reduce therisk that the inner tube 40 might be dislodged from inspiratory port 22,after being bonded thereto during manufacture, outer tube 50 is bondedat its proximal end 52 to the outer wall 29 of patient port 26, and isbonded at its distal end 51 to distal terminal 30.

A New Proximal Terminal

With reference to FIG. 3A, a new and improved proximal terminal 60 isillustrated, which has many surprising advantages over prior artproximal terminals used in unilimb devices. Instead of having threeports, like the proximal terminal 20 of FIG. 2, proximal terminal 60 hasfour ports, which provide advantages and features not possible withprior art artificial ventilation systems. Proximal terminal 60 comprisesa rigid, unitary T-shaped housing. having an inspiratory port 62, anexpiratory port 64, a first respiratory port 66, and a secondrespiratory port 68. Inspiratory port 62 has a step-wise taper from awider-diameter proximal end 63 to a narrow diameter distal end 65,although the taper may be smooth and continuous, or have other shapes.An inner conduit 70, having a proximal end 71 and a distal end 72 issealably connected and bonded to inspiratory port 62 at fitting 74 (dueto the short distance between wider-diameter proximal end 63 and thenarrow diameter distal end 65, and since the inner conduit 70 is bondedinto inspiratory port 62, inspiratory port 62 is considered as a singleport for purposes of describing the invention, rather than described asan external port at wider-diameter proximal end 63 and as an internalport at the narrow diameter distal end 65; thus, the proximal terminal60 is considered to have four ports if the inspiratory port isconsidered as a single port, but may also be considered as having fiveports if the inspiratory port is considered as two ports). In apreferred embodiment, the outer diameter of inner conduit 70 is sealablybonded to distal end 65 of inspiratory port 62, so as to be integraltherewith. An integral annular wall 75 forms the distal end 65 ofinspiratory port 62. First respiratory port 66 and second respiratoryport 68 form concentric ports about axis line 78, preferably havingtheir concentric openings in the same plane which is perpendicular toaxis line 78 of inner conduit 70. Note that second respiratory port 68,while shown axially centered or concentric, within first respiratoryport 66, may be off-center with respect to axis line 78 (although thiswould require that at least a portion of inner conduit 70 to likewise beoff-center with respect to axis line 78). In an alternative embodimentshown in FIG. 3B, inner conduit 70 may axially extend outward slightlyfrom first respiratory port 66 so as to further facilitate connection ofa tube to second respiratory port 68. Optional flanges 76 may beprovided at second respiratory report 68 and/or first respiratory port66 in order to engage matching threads or flanges of detachable tubularfittings which may be attached thereto (additional embodiments ofconnecting fittings are further described below with reference to FIGS.14, 15, 16, and 19). If flexible tubing is to be connected to first andsecond respiratory ports by pressure fit or friction fit, the walls ofthe housing 60 should he sufficiently rigid to permit a firm sealedconnection. The new proximal terminal may be formed of rigid plastic,such as is typically used in rigid attachments to artificial ventilationsystems. Since the new proximal terminal is designed for multi-use, itmay also be formed of metal, such as stainless steel. If the terminal isformed of plastic (such as that used in the UNIVERSAL F™ proximalterminal), it may be clear, translucent or opaque. It is important thatthe walls of the proximal terminal housing near and at the ports havesufficient rigidity to permit connection to conduits, such as thepatient respiratory conduit tubes, and conduits connecting to theinspiratory and expiratory ports.

New Unilimb Artificial Ventilation System, Including New Interface

With reference to FIG. 4, an exploded plan view of an assistedventilation system utilizing the new proximal terminal 60 of FIG. 3A isillustrated. In the embodiment of FIG. 4, a block diagram of aninterface 80 is shown. Proximal terminal 60 is intended to bemanufactured and shipped as a component independent of flexiblebreathing or respiratory conduit(s) which would lead to a patient,rather than being integrally bound (i.e., bonded) during manufacture toflexible respiratory conduits as with prior art unilimb devices.Therefore, it need not be disposed of or sterilized after a single use,and it may be incorporated in a single unit, such as interface 80, alongwith other functional devices 81, 82, 83, and 84, which are illustratedhere in block diagram form for simplicity, or it can be placed before orafter interface 80 (i.e., the new proximal terminal may be a permanentcomponent of an assisted ventilation device or anesthesia machine). Theflexibility of new proximal terminal 60 is illustrated by showing it inblock form 60A. Although four functional devices 81-84 are incorporatedin interface 80, more or less than this number may be used. Functionaldevices may be in the form of readily attachable and detachable modules,so that the ventilation system may be easily modified to meet therequirements of the user. Further, a varying number of optionalfunctional devices, such as devices 85, 86, 87, 88, and 89 may beincorporated in the system, both proximal and distal of proximalterminal 60A.

In the embodiment of FIG. 4, a coaxial breathing conduit 100 (describedin more detail below) is connected at its proximal end to functionaldevices 85 and 86, which in turn are connected to biological filter 90(another embodiment of which is described in detail below). Inspiratoryand expiratory gases must pass through filter 90, thus isolatinginterface 80, and other system components connected proximally of filter90, from contamination (infection) by patient expiratory gases conductedby conduit 100.

In one embodiment devices 85 and 86 may comprise an O₂ controller (forair dilution) and a CO₂ controller (e.g., a rebreathing shunt hole). Areservoir bag (useful during patient transport and/or resuscitation) maybe connected at, distal of, or proximal of filter 90. If the coaxialrespiratory conduit is used for long term care, like in the ICU(intensive care unit and the like), devices 85 and 86 may comprise anebulizer and a water trap. Devices 81-84, 87-89 may likewise performcontrol and/or monitoring functions. For example, devices in modularform can be added so that oxygen can be monitored by an oxygen sensor,and controlled by an air dilution valve; carbon dioxide can be monitoredby a capnometer, and controlled by a rebreathing shunt hole; anestheticgases can be monitored by sensors and controlled by an anesthesiamachine; and temperature and humidity can be monitored by appropriatedevices, and controlled by an artificial nose.

A New Patient Respiratory Conduit

With reference to FIG. 5A, an alternative embodiment of a patientbreathing conduit for use with the proximal terminal of FIG. 3A isillustrated. Breathing conduit 100 consists of a flexible inner tube 110and a flexible outer tube 120, both connected to proximal fitting 130.Inner tube 110 and outer tube 120 are kept in spaced coaxialrelationship at their proximal connection to fitting 130. In oneembodiment, inner tube 110 and outer tube 120 are permanently bonded tofitting 130. Fitting 130 has radial flanges 132 which keep rigid innerpipe 134 connected to but spaced from rigid outer pipe 136. Threads orflanges may be optionally provided on inner pipe 134 and/or outer pipe136 to permit engagement with flanges or threads at second respiratoryport 68 and/or first respiratory port 66, or to permit connection to afilter device, which in turn connects to second respiratory port 68and/or first respiratory port 66.

Distal end 122 of flexible outer tube 120 connects to a rigid annulardistal terminal 124. The distal end 112 of flexible inner tube 110 doesnot axially extend beyond distal terminal 124 or the distal end 122 ofouter tube 120. The distal end 112 of flexible inner tube 110 mayoptionally be connected to distal terminal 124 or to the distal end 122of outer tube 120, or may be free to move axially within outer tube 120.The distance between distal end 112 of flexible inner tube 110 and thedistal end 122 of flexible outer tube 120 (as extended by distalterminal 124) defines a dead space 138. In one embodiment of breathingconduit 100, varying lengths of flexible inner tube 110 and/or flexibleouter tube 120 are utilized in order to vary the size of the dead spaceto a predetermined volume. In another embodiment, outer tube 120 isformed of adjustable-length tubing, so that the dead space can beadjusted by extending or compressing the outer tubing axial length.Extension may be done by adding a dead space tube to the distal end ofouter flexible tube 120, rather than or in addition to using anextendable, accordion-like outer flexible tube. The outer tubing may beformed of transparent or semi-transparent material, and calibrationmarkings 121 may be included thereon to permit determination of deadspace volume by alignment of the distal end 112 of inner tube 110 withthe markings 121.

Distal end 122 of flexible outer tube 120 or distal terminal 124 may beprovided with a positioning device, which may be formed of one or moreinner tapered flanges, or a positioning ramp, with a terminating stop,so that when the distal end 122 of flexible outer tube 120 or distalterminal 124 is biased against the distal end 112 of inner flexible tube110, the distal end 112 of flexible inner tube 110 is positioned at thedesired location with respect to distal end 122 of flexible outer tube120 or distal terminal 124, with the terminating stop preventing distalend 112 of flexible inner tube 110 from extending distally of distal end122 of flexible outer tube 120 or distal terminal 124.

In a preferred embodiment, flexible tubes 110 and 120 are readilyattachable to and detachable from fitting 130, and flexible tube 120 isreadily attachable to and detachable from distal terminal 124. In oneembodiment, flexible tube 110 is not utilized, so that the entire lengthof tube 120 constitutes dead space. In another embodiment, tube 110and/or tube 120 connect directly to an interface, which incorporatesproximal terminal 60; a biological filter is located between theproximal terminal and tubes 110 and 120.

A New Coaxial Filter

With reference to FIG. 6A, a preferred embodiment of a new coaxialfilter device 140 is illustrated, which can be used in a unilimbventilation device. Filter 140 includes an inner housing 150 and anouter housing 160. Inner housing 150 is formed of tubular conduits 152and 154 connected to opposed openings in filter chamber 156, whichcontains a first or inner filter 158. Outer housing 160 is formed oftubular conduits 162 and 164 connected to opposed openings in filterchamber 166, which contains a second or outer filter 168. Flanges orthreads may be provided at one or more of the tubular conduit ends 153,155, 163, and 165, so that the filter may be secured in axialrelationship to other tubular fittings. In a preferred embodiment,filter device 140 is connected to a proximal terminal, such as proximalterminal 60 in FIG. 3A, so that inner tubular conduit 152 is sealablyconnected to the second respiratory port 68 and outer tubular conduit162 is sealably connected to the first respiratory port 66. In apreferred embodiment, inspiratory gases pass into tubular conduit 152,pass through filter 158, and out of tubular conduit 154 into a breathingconduit, such as breathing conduit 100 illustrated in FIG. 5A, leadingto a patient. Expiratory gases pass out of a breathing conduit into theannular spacing between outer tubular conduit 164 and inner tubularconduit 154; the expiratory gases then pass through filter 168, intotubular conduit 162 (i.e., the annular spacing between outer tubularconduit 162 and inner tubular conduit 152), and into the proximalterminal and out of the expiratory port of the proximal terminal, suchas port 64 in proximal terminal 60 in FIG. 3A. The preceding gas flowpattern can be reversed if desired.

In an alternative embodiment shown in FIG. 6B, filters 158 and 168 canbe coplanar, and may even be formed of a single filter disc passing fromthe inner wall of the outer filter chamber through the wall of the innerfilter chamber. In yet another embodiment, inner tubular conduit 152 mayaxially extend from the end 163 of tubular conduit 162; the extension oftubular conduit 152 is sufficiently long to reach and sealably connectto the inspiratory port of a prior art proximal terminal, which lacksthe inner conduit of the new proximal terminal of the present invention.An advantage of the coaxial filter is that one filter device may be usedrather than two, using less space in shipping, use, and disposal.

With reference to FIG. 5B, an optional tubular extension 135 isillustrated which may be connected to end 137 of the inner pipe 134.Extension 135, when connected to end 137 is sufficiently long to reachand sealably connect to the inspiratory port of a prior art proximalterminal, which lacks the inner conduit of the new proximal terminal ofthe present invention.

In a preferred embodiment, the patient, or respiratory, conduitcomprises a flexible tube with a diameter between 22 mm and 28 mm, and alength between 100 cm and 1.5 meters. If an inner tube is used with theaforementioned tube, the diameter (or D) is preferably between 11 mm and15 mm. When using a single tube respiratory conduit, a 22 mm diameter isdesirable for adult use, and a 15 mm diameter is desirable for pediatricuse. When a coaxial conduit is used, a 28 mm diameter outer tube and 15mm diameter inner tube are preferred. Single tube and coaxialrespiratory conduit conventionally have standard slip fittings at atleast one end for connection to other components to be used in anassisted ventilation system.

Dead space volume, V_(D), in a tube is determined by the relationship:

V _(D)=Π(D/2)² ×L,

where L is the length of the dead space, and D is the outer conduit tubediameter. In a preferred embodiment, the first (outer) and second(inner) respiratory ports of the proximal terminal have inner diameterswhich are approximately equal to that of the outer tube and inner tube,respectively. Likewise, the outer and inner conduits at the opposed endsof the coaxial filter have inner diameters which arc preferablyapproximately equal to that of the outer tube and inner tube,respectively; and the outer and inner annuli (i.e., ends of pipes) ofthe proximal fitting have inner diameters which are preferablyapproximately equal to that of the outer tube and inner tube,respectively.

Thus, the present inventor has described a new unilimb artificialventilation system, which includes a new patient conduit, a new coaxialfilter, and a new proximal terminal, the latter of which may beincorporated into a new multifunctional interface. Various advantagesand features of these inventions will be readily apparent to one ofskill in the art; by way of non-limiting examples, these new devices areless expensive to manufacture; are easier to use, and have a wider rangeof uses and configurations than prior art systems; these new devicesreduce medical wastes, since more components can be reused; yet, thesedevices are safer to use, due to the reduction of equipment required atthe patient terminal, and provide for greater monitoring and control.

Artificial Ventilation Which Avoids Hypoxia and Hypocapnia

The unilimb artificial ventilation device of the present invention isideal for providing artificial ventilation to a patient in which hypoxiais avoided while safely avoiding hypocapnia or even providing moderatehypercapnia. It was surprisingly discovered that normal carbon dioxidelevels (normocapnia), or even moderate hypercapnia could be safelyinduced and/or maintained in a patient without causing hypoxia, asdemonstrated by extensive data from human subjects, which dramaticallyillustrates this surprising discovery, and how the unilimb dead spacevolume can be adjusted to achieve normocapnia or moderate hypercapniawithout causing hypoxia.

EXPERIMENTAL

Traditional methods of artificial hyperventilation using large tidalvolume (V_(T)>10 ml/kg) and ventilatory frequency (f>10-12 breaths/min)inevitably result in a marked decrease in arterial blood carbon dioxidetension (PaCO₂), hypocapnia, and is often associated with seriousadverse side effects.

Adverse effects of hypocapnia include: a) Vital organ tissueischemia/hypoxia, since hypocapnia decreases cerebral, myocardial andsplanchnic blood flow, and shifts the oxygen dissociation curve to theleft, making the release of oxygen to the tissues difficult; b)Hypocapnia causes reduction of cardiac output and thus decreases theoxygen delivery (i.e. oxygen supply and availability to the tissues); c)Hypocapnia causes severe vasoconstriction of some tissues such as theskin; d) Hypocapnia causes blood and tissue biochemical disturbances:Anaerobic metabolism increases blood lactic acid concentration; andchanges in plasma electrolytes (sodium, potassium, calcium, etc.) causecardiac arrhythmias, metabolic acidosis, tetany, etc.

Therefore, studies were conducted to investigate the effects ofventilation apparatus dead space (V_(D)) on the arterial blood carbondioxide tension (PaCO₂, “Pa” may be used interchangeably with “P_(a)”),and oxygen tension (PaO₂) during anesthesia. After institutionalapproval and patient consent, a total of 301 healthy (ASA class I) adultpatients undergoing elective surgery were studied (divided into Study Iof 241 patients, and Study II of 60 patients). Anesthesia was inducedwith a sleeping dose of thiopental; endotracheal (ET) intubation wasfacilitated with 1 mg/kg succinylcholine. Anesthesia was maintained with60-70% nitrous oxide in oxygen and 0.5-1.0% halothane, or 0.8-1.5%enflurane, using a conventional anesthesia circle breathing system withCO₂ absorption. Intraoperative muscle relaxation was achieved withintermittent pancuronium bromide as required. The patients' lungs weremechanically ventilated using the traditional mode of intermittentpositive pressure ventilation (IPPV) with the following ventilatorysettings. Tidal volume (V_(T)=10 ml/kg), ventilatory frequency (f=10-12breath/min), and inspiratory/expiratory ratio (I:E ratio=1:2) were keptconstant throughout the study. V_(T) was determined with a Wrightrespirometer placed at the ET tube. Fraction of inspired oxygenconcentration (F_(i)O₂=0.3-0.4) was monitored using a galvanic oxygenanalyzer (Riken OX-160, Japan). End-tidal CO₂ concentration wasmonitored using an infra-red CO₂ analyzer (AIKA, RAS-41, Japan).

After cardiopulmonary stabilization with the traditional mode ofventilation (i.e. no dead space; i.e., dead space external of thepatient of less than 10 ml) was achieved, an arterial blood sample froma radial artery was obtained and immediate analysis of the blood samplewas performed using an ABL2 blood gas analyzer (Radiometer, Copenhagen)for control measurement. After control values were taken, one or two ofthe predetermined dead space volumes, V_(D), selected from 160, 200,350, 510 and 550 (ml) was (or were) chosen randomly, and incorporated inthe breathing circuit while the same artificial ventilation setting wasmaintained for 30 min. Thereafter, blood gas measurements were repeatedfor comparison and statistical analysis was performed. The results ofStudy I of 241 patients are summarized in Table I (divided into Group A,60 kg±17; Group B, 65 kg±9; and Group C, 90 kg±8), and results of StudyII of 60 patients in FIGS. 7-10.

Table 1 shows that the traditional mode of artificial ventilation usingIPPV with no apparatus dead space inevitably resulted in a markeddecrease in arterial carbon dioxide tension (PaCO₂) i.e., hypocapnia.Addition of dead space, V_(D)=160-200 ml, V_(D)=350 ml, and V_(D)=550ml, significantly increased the PaCO₂ to normocapnic and moderatehypercapnic levels respectively, without evidence of substantial PaO₂decreases, i.e. hypoxia, in any of the patients of Groups A, B and C.Study II shows a mathematical regression analysis of the blood gas dataobtained from 60 patients (120 samples) during artificial ventilationwith varied dead space volumes. Thus, it is demonstrated that apredetermined volume of dead space in the breathing

TABLE 1 Arterial Blood Gas Data Obtained From 241 Anesthetized Patients(318 samples) During Artificial Ventilation With or Without ApparatusDead Space (Study I) Number of Body Weight Dead Space Volume (V_(D) inml) Group Patients (Kg) 0 160-200 350 550 A 172 60 ± 17 HypocapniaNormocapnia Moderate Moderate B  61 65 ± 9  Hypercapnia Hypercapnia C  890 ± 13 Group FiO₂ Control PaCO₂ A (0.3) 32 ± 6 (mmHg) B (0.3) 33 ± 4 42 ± 9* C (0.3) 34 ± 7 46 ± 11* 51 ± 8*  PaO₂ A (0.3) 169 ± 40 (mmHg) B(0.3) 163 ± 28 164 ± 22 C (0.3)  178 ± 125 212 ± 116* 217 ± 137* Mean ±SD, *p < 0.05 vs Control (V_(D) = 0); Ventilatory setting: V_(T) = 10ml/kg, f = 10-12 breath/min, I:E ratio = 1:2.

circuit can significantly control the PaCO₂ values without evidence ofhypoxia during artificial ventilation, as illustrated in FIGS. 7-10 andTable 1. Maintenance of normocapnic levels may be highly desirable andbeneficial to the patients during anesthesia and/or to patientsundergoing artificial ventilation, for example in the ICU. As is clearfrom Table 1 and FIG. 10, the vast majority of patients will require anassisted ventilation system having a dead space of at least 100 cc, andin many instances of at least 160 cc, to obtain normocapnia whileavoiding hypoxia, in accordance with the present invention.

FIG. 7 is a graphic illustration of the relationship between dead spacevolume, V_(D), measured in milliliters per kilogram of patient bodyweight (ml/kg, or cubic centimeters per kg of body weight, cc³/kg), andthe resulting change in patient arterial carbon dioxide tension,P_(a)CO₂, (measured in mmHg), including a linear regression analysiscurve, yielding a correlation coefficient, r, of 0.671, and a predictedvalue for the change in P_(a)CO₂ equal to the product of 2.621 times theV_(D), plus 1.766, or in equation form:

ΔP_(a)CO₂(mmHg)=(2.621×V _(D)(ml/kg))+1.766.

This illustrates that the change (Δ) in P_(a)CO₂ can be reliablypredicted as a function of V_(D) (when V_(D) is between 0 and 8 ml perkg of patient weight, or cc³/kg).

FIG. 8 is a graphic illustration of the independence of P_(a)CO₂ asV_(D) is varied between about 0 and 8 ml/kg, including a linearregression analysis curve which shows no significant correlation ® isonly 0.074) between the two variables in the range tested. Thus, evenwhen dead space volume is large enough to increase P_(a)CO₂ by 15 mmHg(see FIG. 7), there is no significant reduction in P_(a)CO₂.

FIG. 9 is a graphic illustration of the independence of changes inP_(a)CO₂ and P_(a)CO₂ as P_(a)CO₂ was varied between 0 and 25 mmHg,including a linear regression analysis curve having a correlationcoefficient, r, of 0.153, thus showing that increasing P_(a)CO₂ between0 and 25 mmHg has no significant effect on P_(a)CO₂.

The table of FIG. 10 is generated by the results of data shown in thegraph of FIG. 7 of Study II.

Thus, the artificial ventilation method of the present inventionprovides for increasing the dead space volume external to a patient toinduce and/or maintain normocapnia or moderate hypercapnia whileavoiding hypoxia. Without limiting the invention to any particulartheory of operation, it is believed that the anatomical dead spacepresent in a patient's respiratory system, including for example thatformed by the upper airway (i.e., nose, mouth, laryngeal cavity),trachea and bronchial trees, is at least partially eliminated byendotracheal intubation devices. Thus, the amount of rebreathing fromthe anatomical dead space is reduced. Further, in order to avoid hypoxiaand atelectasis in the prior art, inspiratory oxygen is provided at highpressure, large tidal volume and rapid respiratory rate; this results inhyperventilation and considerable reduction in concentration of arterialcarbon dioxide.

In a preferred embodiment, the dead space volume in a unilimb patientrespiratory conduit is adjusted to at least 10 ml (cc³), or in analternative embodiment to at least 30 ml, and may be adjusted to or inexcess of 150 ml. The unilimb patient respiratory conduit used may beany of those described herein, or modifications thereto. Although use ofthe devices described herein is preferred for the foregoing artificialventilation method, it is anticipated that the discovery that increasedcarbon dioxide does not necessarily cause hypoxia, so long as sufficientoxygen is provided, may lead to the use of other devices to provideartificial ventilation without hypocapnia or hypoxia. For example,carbon dioxide from an external source may be combined with theinspiratory gases, or a dual limb system may be used, in whichadditional carbon dioxide is supplied to the patient. For example, withreference to FIG. 11, a Y-shaped fitting 180 is illustrated, which hasan input port 182, an exhaust port 184, and a respiratory port 186.Fitting 180 is connected at its distal end to a filter device 190. Oneway valves, not shown, are proximal of ports 182 and 184 to ensureintermittent positive pressure ventilation. A flexible tube 200 isattached at its proximal end 202 to the distal end of filter device 190.Thus, the entire internal volume of tube 200 serves as dead space. Thelength and diameter of tube 200 may be selected to achieve apredetenmined dead space.

Thus, the assisted ventilation method of the current invention, whichavoids hypoxia and hypocapnia, can be provided in some instances witholder assisted ventilation systems, while still having the advantages ofa single tube for inspiratory and expiratory gases. Tube 200 and filterdevice 190 may be sealably bonded together, or separate easilyattachable and detachable components. Tube 200 can be of varyingpredetermined lengths of uniform diameter for preselected dead spacevolume; tube 200 may have axial adjustable length, and have calibrationmarkings at its opposed ends, the distance between the distal andproximal markings thereon precalculated to provide a predetermined deadspace (in one embodiment, distal calibration markings can only be seenwhen the surrounding flexible pleated tubing is axially extended, andare not legible when the surrounding tube pleats are in their foldedaxially compressed state).

In a preferred embodiment, artificial ventilation is provided to amammal (e.g., a human) sufficient to prevent hypoxia, while a sufficientportion of the mammal's expiratory gases are rebreathed to permit thearterial carbon dioxide tension of the mammal to be between about 35mmHg and about 95 mmHg, and, in another preferred embodiment, thearterial carbon dioxide level of the mammal is kept between about 35mmHg and about 45 mmHg (i.e., normocapnia).

With reference to FIG. 12, an alternative embodiment of the presentinvention is illustrated. Unilimb respiratory conduit 100 is connectedat its proximal end to the distal end of proximal terminal 60 viaproximal fitting 130. Unilimb respiratory conduit 100 has a distalterminal 210, to which is connected outer flexible tube 212 at itsdistal end 214. Inner flexible tube 216 is connected at its proximal endto inner pipe 218 of proximal fitting 130. The distal end 220 of innerflexible tube 216 may be free to move axially with respect to the distalend 214 of outer flexible tube 212, or the distal end 220 of innerflexible tube 216 may be connected to distal terminal 210, or the distalend 220 of inner flexible tube 216 may be prevented from extendingbeyond the distal end of outer flexible tube 212 (as possibly extendedby distal terminal 210) by a stop (not shown) in distal terminal 210.

Since the coaxial unilimb respiratory conduit 100 provides theadvantages mentioned above, and may have substantial length so that itmay reach from an assisted ventilation device located remote from thepatient, it is desirable in some instances to reuse the coaxial unilimbrespiratory conduit 100, or to add and/or adjust the dead spaceindependent of coaxial unilimb respiratory conduit 100. Thus, filter 190is detachably connected at its proximal end 192 to distal terminal 210.Filter 190 is detachably connected at its distal end 194 to proximal end202 of flexible tube 200. Flexible tube 200 may have a predetermineddead space, or may have accordion-like folds therein to permitadjustment of the dead space volume. In one embodiment, filter 190 ispermanently bonded to flexible tube 200, and the combination has a fixeddead space (i.e., the volume of the filter and tube combined). Inanother embodiment, calibration marks (such as 121 in FIG. 5A), can beplaced on flexible tube 200, and these calibration marks may take intoaccount the dead space volume of the filter (i.e., the filter volume isadded to the volume of flexible tube 200). Thus, a user may dispose offilter 190 and tube 200 after a single use, and referring to FIG. 13, acombination filter 190 and tube 200 for single use is illustrated.

As is clear from the foregoing, in practice, a new assisted ventilationdevice is made by health care personnel for each patient from newdisposable components in combination with reusable components. Thedisposable components and reusable components forming each assistedventilation system are selected to match the unique needs of eachpatient. Thus, the present invention provides new components, newmethods of providing components, and methods of making assistedventilation systems.

The filter and dead space tube combination is a surprisingly valuableand useful device, as it was previously believed necessary to minimizedead space, yet the dead space in the filter and tube are intentionallymade greater than what the inventors believe to have previously beenprovided. The surprising discovery that dead space can be used toachieve normocapnia or moderate hypercapnia without hypoxia createssubstantial patient health and cost benefits. For example, by use of afilter and dead space tube in connection with an assisted ventilationdevice (e.g., ventilator), sufficient oxygenation can be provided to apatient while maintaining a substantially normocapnic state with asingle tube. In certain instances, only the filter and the single tube(i.e., dead space tube) need be disposed of after use, thus creatingsubstantial cost savings, and reducing medical wastes. In a preferredembodiment, the volume of the dead space in the dead space tube and/orfilter when connected between a patient and an assisted ventilationdevice is sufficient to permit sufficient oxygenation to a patient whilemaintaining a normocapnic or moderate hypercapnic state. Preferably, thedead space volume in the dead space tube and/or the filter is betweenabout 10 cubic centimeters and about 1000 cubic centimeters, and theflexible tubing forming the dead space tube has a diameter between about11 millimeters and about 28 millimeters, and a length between about 5centimeters and 1.5 meters. In an alternative embodiment, the dead spacevolume in the dead space tube and/or the filter is between about 50cubic centimeters and about 1000 cubic centimeters, and the flexibletubing forming the dead space tube has a diameter between about 15millimeters and about 28 millimeters, and a length between about 5centimeters and 1.5 meters.

Thus, instead of requiring two tubes (one inspiratory and the otherexpiratory), a single tube serves as both an inspiratory and expiratoryconduit. The present invention thereby creates a surprisingly beneficialand new method of providing unilimb respiratory conduits for use inproviding assisted ventilation and making assisted ventilation systems,wherein the systems are constructed at the site of use by the user,users, and/or assistants thereto, by use of tubing having apredetermined dead space volume in the assisted ventilation system madefor the patient. In one embodiment, tubing of predetermined fixedvolume, or a range of volumes in the case of adjustable volume tubing(e.g., FLEXITUBE®) is provided to the user. The user merely needs toselect a tube with the desired volume. In another embodiment, tubing maybe sold in coils of great length, and cut to the desired size.Calibration marks may be made on the tubing to permit easierdetermination of the volume in a length thereof. The latter method is ofcourse slower, and there is more room for human error. Thus, it isbelieved that health care personnel will prefer to use sections oftubing available at the site of use having premeasured standard volumes,or volume ranges, and the sections of tubing will preferably have eitherintegral or attached fittings thereon to facilitate fabrication of theassisted ventilation system and operable connection to a patient.

In addition to providing new methods of making assisted ventilationsystems, the present invention includes tubing for use in makingassisted ventilation systems, of the new type described herein having adead space therein sufficient that when used to provide assistedventilation to a mammal maintains normocapnia or moderate hypercapniawithout hypoxia, wherein the tubing has the length and diameterparameters needed to create the desired dead space volume and/or rangeof volumes. Thus, also included in the present invention are methods ofproviding tubing to users at the site of use for use in making suchassisted ventilation systems.

COMPONENTS AND METHODS TO ENHANCE PATIENT SAFETY

One of the objects of the present invention, and modern medicine ingeneral, is reducing biological and other types of contamination. asfrequently there are greater health effects to patients from infectionthan from their underlying injuries. Filters create a barrier tocontamination from a patient and the surroundings entering assistedventilation devices, and likewise create a barrier to any contaminationin assisted ventilation devices from being breathed in by patients.Nevertheless, it is possible that in the rush and pressure of assistingpatients, a fresh filter will not be attached for each patient, or, insome cases, filters not meeting minimum filtration standards will beused. Further, while it may be desirable in some instances to reuse thecoaxial patient respiratory conduit by using the disposable filter anddead space tube embodiment shown in FIGS. 12 and 13, after a period oftime, moisture, nebulized pharmaceutical agents, and other chemicals mayprecipitate in the coaxial conduit, and/or contaminants may build uptherein. Thus, referring to FIG. 12, it is desirable in some instancesto ensure that coaxial unilimb respiratory conduit 100 is disposed ofafter a single use along with filter 190 and tube 200. In an alternativeembodiment, a coaxial filter, such as that illustrated in FIGS. 6A or 6Bmay be inserted in the device of FIG. 12, wherein the proximal terminal60 is separated from and operably connected to the coaxial unilimbrespiratory conduit 100 by the coaxial filter of FIG. 6A or 6B.

Thus, with reference to FIGS. 12, 14, 15, 16, and 19, non-limitingexamples of unique fittings are illustrated, which can be utilized toensure that proper connections are made to proper devices, all with thedesign of maximizing patient well being, while also minimizing costs.Referring back to FIG. 12, filter 190 is detachably connected at itsproximal end 192 to distal terminal 210. The cylindrical proximalterminating portion or proximal sleeve 193 of proximal end 192 has aninner diameter sized to friction fit over the outer diameter of thedistal terminating portion or male fitting 211 of distal terminal 210.Either or both of proximal sleeve 193 and male fitting 211 may betapered to facilitate connection therebetween; in another embodiment,the proximal sleeve 193 (or female fitting) and male fitting 211 havemating frustoconical shapes. By adjusting the size of proximal sleeve193 and male fitting 21 , only components, such as dead space tubes withpredetermined specifications (or patient airway devices, e.g.,endotracheal tubes, laryngeal and other masks) having the proper sizedproximal sleeves may be connected to a coaxial unilimb respiratoryconduit such as that illustrated in FIG. 12.

With reference to FIG. 14, an alternative embodiment of the presentinvention is illustrated, in which filter 190 is integrally connected toa proximal connector fitting 240. Filter 190 may also be a combinationfilter and HME device (heat and humidity exchanger). A partial crosssection of cylindrical sleeve 242 is shown to permit a side view ofhooks 244 (all connector fitting sleeves may be tapered orfrustoconically shaped to facilitate connection). Referring to FIG. 15,an end elevation view of a distal connector fitting 250 for use inalternative embodiments of the present invention is illustrated. It isenvisioned that all distal connectors may be used as proximal connectorsand vice versa, and thus, the distinction between distal and proximalconnector fittings is merely to facilitate description thereof. Thefitting 250 may be, by way of non-limiting examples, integrallyconnected at the distal end of distal terminal 124 in FIG. 5A and 5B ordistal terminal 210 in FIG. 12, or integrally connected at the distalend of proximal terminal 60, for example in place of flanges 76 on thedistal end of the inner conduit 70, or may be integrally connected tothe distal end of the outer conduit in FIG. 3A.

A plurality of inwardly facing flanges 252 are provided to blockattempts to insert the ends of tubes or other devices, such asinappropriate dead space tubes and/or filters, into distal connectorfitting 250. Thus, only devices which have a mating fitting, such as forexample proximal connector fitting 240, can be connected to distalconnector fitting 250.

With reference to FIG. 16, an adapter comprising proximal connectorfitting 240 is illustrated. Hooks 244 are annularly arranged about andconnected to inward facing annular flange 246. A cylindrical sleeve 248projects proximally from fitting 240, and has an inner diameter whichapproximately matches the outer diameter of distal connector fitting 250(i.e., sleeve 248 and connector fitting 250 are shaped and sized topermit sleeve 248 to slidingly and sealably engage connector fitting250). For example, the proximal edge 249 of cylindrical sleeve 248 maybe tapered out to a larger diameter, and/or the distal edge 251 ofdistal connector fitting 250 may be tapered inward to a smaller diameterto facilitate a sealing slip connection of sleeve 248 over the distaledge 251. An annular flange 254 is connected near or at distal edge 251in distal connector fitting 250 by tabs 256, thus creating an annularpattern of openings 258 about the periphery of annular flange 254.

Hooks 244 are formed of fingers 260 which project axially and proximallyfrom annular flange 246, and terminate in retaining flanges 262. Byaxially aligning the proximal end of proximal connector fitting 240 withthe distal end of distal connector fitting 250, hooks 244 may be alignedand inserted into openings 258. Counterclockwise rotation of fitting 240with respect to fitting 250 causes one or more retaining flanges 262 tobe latched behind one or more tabs 256, thus creating a more secure sealand grip between the fittings. Optional barbs or teeth 264 are shown inFIG. 16. In a preferred embodiment, when teeth 264 are used, the lengthof fingers 260 is just sufficient to axially project the retainingsurface 265 of retaining flanges 262 so they may engage the proximalsurface of tabs 256 when fitting 250 is fully axially inserted intofitting 240 and rotated. The teeth 264 have a tapered surface 266 tocreate a ramp, and hooks 244 and annular flanges 246 and 254 aresufficiently resilient to permit the teeth to slide over the proximalsurface of tabs 256 upon relative counterclockwise rotation of fittings240 and 250 and to thereby latch thereon. Each tooth has a lockingsurface 268, which permits the tooth to snap into the openingimmediately counterclockwise of the opening in which its correspondinghook was inserted, which may provide a tactile and/or audible indicationthat the two fittings are fully engaged. Although hooks 244 areillustrated herein to permit the engagement of teeth 264 with tabs 256upon relative counterclockwise rotation of fittings 240 and 250, theopposite arrangement is also contemplated. The ability to releasablylock fittings 240 and 250 together is dependent on the resilience ofhooks 244 and annular flanges 246 and 254, the length of teeth 264, andthe interaction of each locking surface 268 with the correspondingsurface on the tab to which it is engaged. Thus, in one embodiment,teeth 264 serve to indicate that the fittings are fully engaged, whilein another embodiment, the teeth 264 prevent the fittings 240 and 250from being readily disconnected after the teeth are locked in place.

With regard to FIG. 19, a male threaded fitting 280 and female threadedfitting 290 are illustrated. In this alternative embodiment,corresponding threaded fittings permit only matching components to beattached. For example, threaded fitting 280 may be integrally attachedor bonded to the distal end of the inner conduit 70 of proximal terminal60. Only filters, tubing and/or other devices have a mating threadedfitting 290 at the proximal end thereof may be connected to threadedfitting 280.

As is apparent from the foregoing, manufacturers of filters, patientairway devices (e.g., masks, endotracheal tubes, etc.), HMEs, watertraps. nebulizers, etc., provided they meet minimum standards, mayproduce such devices with the appropriate fitting 240 or 250 integrallyconnected thereto, depending respectively if it is to be connected tofitting 250 or 240, or analogously fittings 280 and 290 or otherappropriate matching fittings may be used. In order to retrofit devicesmeeting minimum standards, adaptors, such as that shown in FIG. 16, maybe provided, which have a mating connector at one end for the patientrespiratory conduit or other device to which they are to be connected,and having a standard slip connector on the other end to attach to thedevice to be retrofitted. In a preferred example, adapters, such asshown in FIG. 16, have a first end 269 meeting international standardsand a second end meeting the particular fitting requirements.

As is implicit and/or explicit from the foregoing, numerousconfigurations of assisted ventilation systems are embodied in thepresent invention. For example, with reference to FIG. 17, analternative embodiment of the present invention is illustrated whichuses a prior art dual hose fitting 310 connected at its proximal ends totwo filters 302 and 304 and at its distal end to a single tube patientconduit 300. In view of the surprising discovery that dead spacecontained within the single tube patient conduit (along with whateverdead space exists in the dual hose fitting and the other devices in theassisted ventilation system) can be utilized to simultaneously preventhypocarbia while providing sufficient oxygenation, it is envisioned thatsingle tube patient conduits (also referred to herein as dead spacetubes), each having a predetermined dead space volume, or each having arange of dead space volumes, will be provided as a separate components.Note that due to the proximal placement of filters 302 and 304, bothfilters and all components distal thereof will be contaminated bycontact with a patient, and thus may require disposal and/orsterilization after each use.

In accordance with the present invention, a method is provided in oneembodiment to cut tubing from a much longer length, perhaps a roll orcoil, to the desired length at the site of use to achieve a desired deadspace volume, or range of safe volumes in the cases of pleated tubing(e.g., FLEXITUBE®). By having tubes of predetermined volumes ready,there is less likelihood of a mistake being made in cutting tubing to adesired length, and also increases the safety and rate of making anassisted ventilation device in accordance with the present invention.

FIG. 18 is a plan view of an assisted ventilation system using a priorart dual hose fitting 310 connected to a single patient conduit 312 atits distal end (dead space tube), and having a filter 320 connected atthe distal end of conduit 312. In this embodiment, only one filter 320is used, which may provide for less waste, as it is possible, in certaininstances, to only dispose of filter 320 after use, without disposing oftube 312 and fitting 310. Dead space tube may also be referred to as anormocapnic (or moderate hypercapnic) breathing tube, with it beingunderstood that such tubes in accordance with the present invention havea predetermined volume, or range of volumes, sufficient to preventhypoxia when utilized to provide assisted ventilation while alsomaintaining normocapnia or a desired level of carbon dioxiderebreathing.

With reference to FIG. 20, proximal terminal 60, as described in moredetail above with reference to FIG. 3A is connected to a single patientconduit 340. Thus, the entire volume of conduit 340 is dead space. Inthis embodiment, proximal terminal 60 and conduit 340 are not protectedby a filter. Thus, it is anticipated that the embodiment of FIG. 20would be used with a filter 360, and/or with two separate filtersattached to the inspiratory gas inlet and expiratory gas outlet. FIG. 21shows a proximal terminal 60 connected to the proximal end of a patientconduit 340 with a filter 360 connected to the distal end of conduit340. In the case shown in FIG. 20, it may be possible to reuse proximalterminal 60 and conduit 340 by only attaching a fresh filter 360. FIG.22 shows a proximal terminal 60 connected to the proximal end of afilter 360 with a patient conduit 340 connected to the distal end offilter 360. In the case shown in FIG. 21, it may be possible to reuseproximal terminal 60 by attaching a fresh filter 360.

Because of the features of proximal terminal 60, in one embodiment,proximal terminal 60 forms part of, and is integral with, the reusablecomponents of an anesthesia machine and/or assisted ventilation device.When proximal terminal 60 forms part of, and is integral with, thereusable components of an anesthesia machine and/or assisted ventilationdevice, it is preferably provided with means for preventing connectionthereto without proper filtration means. Thus, unique connectorfittings, such as those illustrated in FIGS. 15, 16 and 19 may beutilized. In a preferred embodiment, all components, including at leastone filter, operably attached to proximal terminal 60 are disposable andlockingly engaged together, thus ensuring that patient safety ismaximized by requiring disposal of all of the disposable componentstogether after a single use. For example, by providing proximal terminal60 with a unique distal connector, only a proper filter, having a matingproximal connector, can be attached thereto. Likewise, the filter isprovided with a unique distal connector, which permits only permanentlocking engagement with single use tubing and/or devices leading to thepatient. After use, the filter and components connected thereto aredisposed of, since the permanent locking engagement of the componentsprevents disengagement thereof without damage thereto. Proximal terminal60 can have other shapes than that illustrated herein. For example,additional ports and conduits can be added thereto, the shape of thehousing altered, and the location of ports and conduits connectedthereto altered.

While preferred embodiments of the invention have been illustrated anddescribed in detail in the figures and foregoing description, the sameis to be considered as illustrative and not restrictive in character.For example, while tubes of circular cross-section are used herein, itis anticipated that tubular conduits of varying cross-sectional shapemay be used, and that the inner tube of a coaxial tube may or may not beaxially centered within the outer tube, or only portions of the innertube may be axially centered in the outer tube while other portions maybe off center. It is also envisioned that the proximal terminal may havemore than two conduits passing therethrough, which may connect to aflexible respiratory conduit having more than two lumens. In place ofthe push, twist and lock fittings of the present invention, springbiased clips may be provided on the distal end of one component, whichsnap onto corresponding tabs on the proximal end of another component,or vice versa (the tabs and/or clips may have tapered surfaces so that,when pressed against each other, the clips will bend in order to receivethe tabs). Thus, it is understood that only the preferred embodimentshave been shown and described, and that all changes and modificationsthat come within the spirit of the invention are desired to beprotected.

what is claimed is:
 1. An assisted ventilation system for use in mammalsto provide thereto and exhaust therefrom respiratory gases, comprising:a first breathing conduit for providing and exhausting respiratory gasesfrom a mammal, said first breathing conduit having a proximal end and adistal end and being flexible and axially extendable and compressible toprovide a variable deadspace, interface means for providing gases to beinspired and for receiving expired gases, said interface meanscomprising a proximal terminal operably connected to said proximal endof said first breathing conduit, means for preventing biologicalcontamination from communication with said interface means, said meansfor preventing biological contamination being operably connected to saidfirst breathing conduit, said proximal terminal comprising a rigidhousing, said housing comprising an inspiratory gas input, an expiratorygas outlet, and a first respiratory port, said inspiratory gas input andsaid expiratory gas outlet being in fluid communication with said firstbreathing conduit via said first respiratory port when said breathingconduit is in operable connection with said interface means, whereinsaid first breathing conduit is operably detachable from said interfacemeans for disposal or sterilization after use by a user at the site ofuse.
 2. A unilimb respiratory conduit for use in an assisted ventilationsystem, comprising: an outer flexible tube, an inner flexible tube, saidouter flexible tube and inner flexible tube each having a proximal endand a distal end; the outer diameter of said inner flexible tube beingsmaller than the inner diameter of said outer flexible tube, said innerflexible tube being at least partially disposed within said outerflexible tube, said distal end of said inner flexible tube beingdisposed within and in direct fluid communication with said outerflexible tube, and a proximal fitting, said proximal fitting comprisingan inner pipe and an outer pipe maintained in fixed coaxial spacedrelationship by spacing means, said outer pipe and inner pipe eachhaving a proximal end and a distal end, wherein said distal end of saidinner pipe is operably connected to said proximal end of said innerflexible tube and said distal end of said outer pipe is operablyconnected to said proximal end of said outer flexible tube, saidproximal end of one of said pipes capable of being operably connected toan inspiratory gas input while said proximal end of the other one ofsaid conduits is operably connected to an exhaust outlet, and whereinsaid distal end of said outer flexible tube can be operably connected toan airway device connected to a mammal, and wherein a user may utilizesaid unilimb respiratory conduit in an assisted ventilation system viaoperative connection thereto via said proximal fitting in order to usesaid unilimb respiratory conduit to provide inspiratory gases andexhaust expiratory gases from a mammal, and may disconnect said unilimbrespiratory conduit from the assisted ventilation system after use bydetaching said proximal fitting, and further comprising: filter means,and a dead space tube, said dead space tube having a distal end and aproximal end, wherein said proximal end of said dead space tube can beoperably connected through said filter means to said distal end of saidouter flexible tube, wherein, when said proximal end of said dead spacetube and said filter means are operably connected to said distal end ofsaid outer flexible tube, said distal end of said unilimb respiratoryconduit is operably connected to a mammal, and said proximal end of saidunilimb repiratory conduit is operably connected to a source ofinspiratory gases, inspiratory and expiratory gases may pass throughsaid filter means, and inspiratory and expiratory gases may mix in saiddead space tube.
 3. A respiratory conduit device for use in an assistedventilation system, comprising: a flexible tube and a filter, said tubehaving a proximal end and a distal end, wherein said proximal end may beplaced in fluid communication with a source of inspiratory gas throughsaid filter means and said distal end may be placed in fluidcommunication with a mammal to provide a conduit for inspiratory andexpiratory patient gases, or said distal end may be placed in fluidcommunication with a mammal through said filter means and said proximalend may be placed in fluid communication with a source of inspiratorygas to provide a conduit for inspiratory and expiratory gases, whereinsaid respiratory conduit device can be operatively connected by a userat the site of use to an assisted ventilation system and detached by auser after use for independent sterilization or disposal, wherein, whensaid device is operably connected to a mammal, dead space containedwithin that portion of said respiratory conduit device external of themammal is between about 40 cubic centimeters and about 1000 cubiccentimeters.
 4. The respiratory conduit device of claim 3, wherein saidflexible tube has a diameter between about 15 millimeters and about 28millimeters and a length between about 5 centimeters and about 1.5meters, and is axially extendable and compressible to provide a variabledeadspace.
 5. The respiratory conduit device of claim 3, wherein saidflexible tube has calibration markings that permit determination of thevolume of the dead space within said device.
 6. A method of providingunilimb respiratory conduits for use in assisted ventilation systems,comprising the step of: providing at least one unilimb respiratoryconduit to at least one user for use thereby in administering andexhausting gases from a mammal, wherein said unilimb respiratory conduitcomprises a flexible tube that can be readily operably connected at afirst end to a mammal and at a second end to a terminal housing formingpart of an assisted ventilation system by the user for administering andexhausting respiratory gases from the mammal, said unilimb respiratoryconduit being readily disconnected from the terminal housing after use,said unilimb respiratory conduit for use with a terminal housing havingat least two independent flow paths therein which are capable ofsimultaneous operative connection to a respiratory conduit and whichdiverge to form an inlet port at a second location and an outlet port ata third location in the terminal housing, said second end of saidunilimb respiratory conduit being operably connectable to the firstlocation in the terminal housing, wherein said unilimb respiratoryconduit can be provided with or separately from the terminal housing,said flexible tube being axially extendable and compressible to providea variable deadspace therein, wherein, when said unilimb respiratoryconduit is operably connected to a terminal housing and to a mammal sothat inspiratory gases to and expiratory gases from the mammal passtherethrough, the dead space volume in said unilimb respiratory conduitis sufficient to maintain the mean arterial carbon dioxide tension ofthe mammal between about 35 mmHg and about 95 mmHg without causinghypoxia in the mammal.
 7. The method of claim 6, wherein said unilimbrespiratory conduit is provided for single use, and the terminal housingfor which said conduit is provided for use therewith is reusable.
 8. Themethod of claim 6, further comprising the step of providing a filterwhich may be readily operably connected to and disconnected from saidrespiratory conduit to create a barrier to biological contamination ofthe terminal housing from a mammal when a mammal is to be operablyconnected to said respiratory conduit and the terminal housing.
 9. Themethod of claim 6, wherein said unilimb respiratory conduit comprisescalibration means for determining the dead space therein.
 10. The methodof claim 6, wherein said at least one unilimb respiratory conduit isprovided to one of the group consisting of a health care provider, anICU, and a location where surgery can be performed.
 11. A unilimbrespiratory conduit for use in an assisted ventilation system,comprising: a respiratory conduit which can be operatively connected bya user at the site of use to an assisted ventilation system and detachedby a user after use for independent sterilization or disposal, saidrespiratory conduit comprising a flexible tube having a first end and asecond end, wherein said first end can be operably connected to a mammaland said second end can be operably connected to an assisted ventilationsystem to carry inspiratory gases to the mammal and to receiveexpiratory gases from the mammal, wherein said tube has a variablelength for permitting a user to vary the dead space volume of saidrespiratory conduit by axial extension or contraction thereof, whereinsaid flexible tube has a diameter between about 11 millimeters and about28 millimeters, and a length between about 5 centimeters and about 1.5meters wherein, when said respiratory conduit is operably connected intoan assisted ventilation system and said system is operably connected toa mammal, said respiratory conduit has a dead space volume external ofthe mammal that can be adjusted to exceed about 40 cubic centimeters andto be less that about 1000 cubic centimeters.
 12. The respiratoryconduit of claim 11, wherein said unilimb respiratory conduit hascalibration markings that permit determination of the volume of the deadspace within said unilimb respiratory conduit.
 13. The respiratoryconduit of claim 11, wherein said tube contains at least one of thegroup consisting of an anesthetic gas, and oxygen provided via anassisted ventilation system.
 14. The respiratory conduit of claim 13,wherein said tube is operatively connected to an assisted ventilationsystem.
 15. The respiratory conduit of claim 11, wherein said tube isoperatively connected to an assisted ventilation system.
 16. Therespiratory conduit of claims 11, wherein when said tube is operablyconnected into an assisted ventilation system and to a mammal so thatinspiratory gases to and expiratory gases from the mammal passtherethrough, the dead space volume in said unilimb respiratory conduitis sufficient to maintain the mean arterial carbon dioxide tension ofthe mammal between about 35 mmHg and about 95 mmHg without causinghypoxia in the mammal.
 17. The respiratory conduit of claim 11, wherein,when said tube is operably connected into an assisted ventilation systemand to a mammal so that inspiratory gases to and expiratory gases fromthe mammal pass therethrough, the dead space volume in said unilimbrespiratory conduit is greater than 100 cubic centimeters and less thana volume which will cause hypoxia in the mammal.
 18. The respiratoryconduit of claim 11, wherein, when said tube is operably connected intoan assisted ventilation system and to a mammal so that inspiratory gasesto and expiratory gases from the mammal pass therethrough, the deadspace volume in said unilimb respiratory conduit is greater than 160cubic centimeters and less than a volume which will cause hypoxia in themammal.
 19. An assisted ventilation system, comprising a respiratoryconduit for carrying inspiratory gases to a mammal and for exhaustingexpiratory gases therefrom, wherein, when said system is operablyconnected to a mammal, said system has a dead space volume external ofthe mammal in excess of about 100 cubic centimeters, said dead spacevolume being less than a volume which will cause hypoxia in the mammal,wherein said respiratory conduit can be operatively connected by a userat the site of use into said assisted ventilation system and detached bya user after use for independent sterilization or disposal, saidrespiratory conduit comprising a flexible tube having a first end and asecond end, wherein said first end can be operably connected to a mammaland said second end can be operably connected into said assistedventilation system to carry inspiratory gases to the mammal and toreceive expiratory gases from the mammal, wherein said tube has avariable length for permitting a user to vary the dead space volume ofsaid respiratory conduit by axial extension or contraction thereof,wherein said flexible tube has a diameter between about 11 millimetersand about 28 millimeters, and a length between about 5 centimeters andabout 1.5 meters.
 20. An assembly for use in providing inspiratory gasesto a patient and receiving expiratory gases therefrom, comprising arespiratory conduit and a proximal terminal, said respiratory conduithaving a distal end and a proximal end and said proximal terminal havinga distal end and a proximal end, wherein said distal end of saidrespiratory conduit is operatively connectable to and detachable from apatient by a user at a site of use, and said proximal end of saidconduit is operatively connectable to and detachable from said proximalterminal by a user at a site of use, wherein said proximal terminal hasfirst and second lumens defining respective first and second flow paths,said first and second lumens being independent of each other and eachhaving a distal end and a proximal end, said distal ends of said lumenscapable of simultaneous operative connection to said proximal end ofsaid respiratory conduit and wherein said first and second flow paths insaid proximal terminal diverge from each other proximally of said distalend of said proximal terminal so that said proximal end of said firstlumen may be independently operatively connected to an inlet for asource of inspiratory gas while said proximal end of said second lumenmay be independently operatively connected to an expiratory outlet,wherein said respiratory conduit may be operatively detached from saidproximal terminal after use therewith for independent disposal orsterilization.
 21. The assembly of claim 20, further comprising a commonlumen, wherein said first flow path and said second flow path mergetogether at the distal ends of said lumens to form a common flow path,wherein said common lumen can be placed in operative fluid communicationwith said respiratory conduit.
 22. The assembly of claim 20, whereinsaid first lumen and said second lumen are coaxial in said distal end ofsaid proximal terminal and said third and fourth lumens are formed bycoaxial tubes.
 23. The assembly of claim 20, wherein said proximalterminal is permanently connected to an anesthesia machine or to arespirator type device, wherein a respiratory conduit may be operativelydetached from said anesthesia machine or respirator type device afteruse therewith for disposal or sterilization.
 24. A method forconstructing a breathing circuit having a proximal terminal and arespiratory conduit, wherein the respiratory conduit has a distal endand a proximal end, the distal end of the conduit being operativelyconnectable to and detachable from a patient by a user at a site of use,and the proximal end of the conduit is operatively connectable to anddetachable from a proximal terminal by a user at a site of use, andwherein the proximal terminal has first and second lumens defining firstand second flow paths that are independent of each other and converge ata distal end of the proximal terminal so as to be capable ofsimultaneous operative connection to the proximal end of the respiratoryconduit and wherein the first and second flow paths in the proximalterminal diverge from each other proximally of the distal end of theproximal terminal so that the first lumen of the proximal terminal maybe independently operatively connected to an inlet for a source ofinspiratory gas while the second lumen of the proximal terminal may beindependently operatively connected to an expiratory outlet, and whereinthe respiratory conduit has third and fourth lumens definingrespectively a third flow path and a fourth flow path, the third flowpath and the fourth lumen being independent of each other and eachhaving a distal end and a proximal end, said method comprisingoperatively connecting the respiratory conduit to the proximal terminalso that the distal end of the third lumen is placed in fluidcommunication with the proximal end of the first lumen and the distalend of the fourth lumen is placed in fluid communication with theproximal end of the second lumen so that said third lumen may beoperatively connected to an inlet for a source of inspiratory gas viathe proximal terminal while said forth lumen may be operativelyconnected to an expiratory outlet via the proximal terminal, saidoperatively connecting of the respiratory conduit to the proximalterminal step permitting for the respiratory conduit to be detached fromthe proximal terminal at a site of use for disposal or sterilization ofthe respiratory conduit independent of the proximal terminal.